1. Field of the Invention
The present invention relates to a biodegradable disposable syringe and more particularly, to the biodegradable disposable syringe by using a novel polyester resin composition under a specific injection molding condition, thus being able to be disposed of without causing environmental contamination.
2. Description of the Related Art
In general, biodegradable resins have been welcomed worldwide since they can be disposed of without causing environmental contamination and thus their uses are on the gradual increase these days.
There have been known various kinds of biodegradable resins, however, they have not been applicable to commercial products because either their applications were too limited or their physical properties and biodegradability were not well qualified for good molding and quality products.
The aliphatic polyester, known to have a good biodegradable property (J of Macromol. SCI-Chem., A-23(3), 1986, pp. 393-409), have been used as materials in medical, agricultural, fishing and packaging industries and its fields of applications are on gradual growth. However, the conventional type of aliphatic polyesters had disadvantages that their backbone structures were too soft and heat-labile, it had low crystallinity, low melting point, difficulty in molding due to high melt index, poor tensile strength and tear strength. To make these aliphatic polyesters more applicable, many efforts have been exerted to increase the number average molecular weight of the current aliphatic polyester to have more than 30,000, however, it has not been able to obtain aliphatic polyester having a molecular weight greater than 15,000 in the conventional polycondensation system.
As a way to solve these problems conventional polyesters, a method of manufacturing aliphatic polyester resin having a number average molecular weight of greater than 30,000 by adjusting factors such as reaction temperature, degree of vacuum and amount of catalysts was disclosed in Korean Unexamined Patent Publication No 95-758; however, said aliphatic polyester resin had a low weight average molecular weight and was also heat-labile thus not considered appropriate in molding or forming.
In Korean Unexamined Patent Publication No 95-114171, a method of manufacturing aliphatic polyester with a high molecular weight by incorporating a monomer such as a polyhydric alcohol or a poly (at least tri-) hydric carboxylic acid is disclosed. The above process provided a way to improve the molding and forming properties of the aliphatic polyester resin by introducing the monomers into the reactor to reduce the reaction time and to diffuse the molecules within the product. However, the application of this type of polyester resin was not easy due to the decrease of physical properties such as tensile strength resulted from the drastic increase in low molecular weight polyesters. Besides, the fact that the polyester resin easily becomes a gel type makes it difficult to control the reaction for preparing the polyester resin. There is still another process for increasing the molecular weight of the aliphatic polyester resin. Unexamined Korean Patent Publication No. 95-25072, which discloses the high molecular weight aliphatic polyester resin produced by an isocyanate as a coupling material reacting to an aliphatic polyester resin having a number average molecular weight of 15,000 to 20,000 which is produced by dehydration or de-glycol reaction of the mixture of main materials of (1) an aliphatic(including cyclic type), and (2) an aliphatic (including cyclic type) dicarboxylic acid(or an anhydride thereof) with or without (3) a little of monomer of polyhydric alcohol or polyhydric carboxylic acid (or acid anhydride thereof). The aliphatic polyester resin obtained in this way had a number average molecular weight of 20,000 to 70,000. However, the above-mentioned process has a few drawbacks that it requires more reaction time thus resulting in poor productivity, and the isocyanate, a coupling material to increase the molecular weight of polyester resin, is known to be a carcinogen so necessitating an extremely careful handling of the ingredient.
On top of that there has not been found a good resolution how to deal with the waste disposal of syringes nor the syringes ever manufactured by using biodegradable polyester resins.
The conventional disposable syringes used in medical fields have been a cause of environmental contamination while its biodegradable versions have been experiencing the limited applications due to their poor physical properties. The object of the invention is therefore to provide a disposable syringe which can not only be degraded in nature without causing an environmental contamination but be applied in a broader field of medical industry by having superior physical.